I agree that the Wiimote control scheme you have outlined works in principal, and it would indeed be a fun and creative way in order to control SSB characters. Being a reasonably seasoned player with SSB (7000 game minutes min per character in a house with 3 Uni students, resutling in 2 worn out discs, and now onto our 3rd, we have wasted a lot of our lives on this game, and not sure how they "wore out" but they don't read anymore) the thing you realise with the GC control scheme is that the speed at which you can deliver your moves is intrinsically tied into buttons. For example, with Fox you want the fireball attack down, hit the ground and roll away, followed by a roll back, followed by a smash attack, etc, etc. Buttons allow you to execute these moves extremely rapidly. This is something the Wiimotes IR sensing and motion sensing capabilities cannot allow you to do with the same precision and speed. Compare how long a button combination takes to execute to the Wiimote control scheme you have outlined? If you have to move the Wiimote/Cursor combo in a circular motion around your character on screen and then press a button at the end of this to execute the move as opposed to B+stick direction to execute a similar special move the timings are longer for the Wiimote move. As i'm sure many a SSB player atests to, timing is essential. Could this be overcome with the Wiimote/nunchuk? I believe it could be. Mapping GC controls to Wiimote/nunchuk might be as simple as A/B for standing attack, B+direction flick for moves, A+ direction flick for special moves, Analog stick for movement/jump, C button for shield/block, C+ Nunchuck direction flick for roll, Z for grab/pick up/throw object, etc (i could continue to think on this but i i'm too tired) But you should be able to see the essence of what i'm trying to explain.
For all those that think the Wiimote/nunchuk has limited button options look at the controller in this light, the motion sensing on Wiimote/Nunchuck gives you 2 analog sticks, or two D-Pads (where a Dpad direction press is equal to a quick flick) you then have another analog stick, and then two buttons per hand C/Z, A/B, and finally a D Pad. You could argue to disclude the DPad from this equation as it is not always easily accessible, but even so the possibilities are there without this. And this doesn't even conisder the +/- buttons or the 1/2 buttons. I'm sure there is more i can add, and i'm sure there are holes in my argument, but i'm too tired to really think anymore on this.
Either way, whether it is a Wiimote/Nunchuk or classic/GC controller for SSB, i'm still looking forward to it, and i'm sure Ninty will do a decent job of it.